Field of the Invention
The present invention related to wireless communication and, most particularly, to a sidelink operation method being performed by a user equipment in a wireless communication system and a user equipment using the same.
Related Art
In International Telecommunication Union Radio communication sector (ITU-R), a standardization task for International Mobile Telecommunication (IMT)-Advanced, that is, the next-generation mobile communication system since the third generation, is in progress. IMT-Advanced sets its goal to support Internet Protocol (IP)-based multimedia services at a data transfer rate of 1 Gbps in the stop and slow-speed moving state and of 100 Mbps in the fast-speed moving state.
For example, 3rd Generation Partnership Project (3GPP) is a system standard to satisfy the requirements of IMT-Advanced and is preparing for LTE-Advanced improved from Long Term Evolution (LTE) based on Orthogonal Frequency Division Multiple Access (OFDMA)/Single Carrier-Frequency Division Multiple Access (SC-FDMA) transmission schemes. LTE-Advanced is one of strong candidates for IMT-Advanced.
There is a growing interest in a Device-to-Device (D2D) technology in which devices perform direct communication. In particular, D2D has been in the spotlight as a communication technology for a public safety network. A commercial communication network is rapidly changing to LTE, but the current public safety network is basically based on the 2G technology in terms of a collision problem with existing communication standards and a cost. Such a technology gap and a need for improved services are leading to efforts to improve the public safety network.
The public safety network has higher service requirements (reliability and security) than the commercial communication network. In particular, if coverage of cellular communication is not affected or available, the public safety network also requires direct communication between devices, that is, D2D operation.
The D2D operation may have diverse advantages in the aspect of performing signal transmission/reception between close-ranged devices. For example, a D2D device (or D2D UE) may perform data communication at a high transmission rate with low latency. Also, the D2D operation may disperse (or distribute) the traffic being concentrated to the base station, and, if the D2D UE performs the functions of a relay station, the D2D UE may also perform the function of expanding the coverage of the base station.
The D2D operation is differentiated from the operation performed between a UE and a base station (network) in a cellular link, based on the aspect of the D2D operation being performed in a link between a UE and another UE. Hereinafter, the link between UEs will be referred to as a sidelink, and the D2D operations may also be referred to as sidelink operations.
When a UE performs sidelink operations, the operations performed in the cellular link may be limited. For example, it may be difficult for a UE being equipped with only one reception chain to receive a signal according to a cellular communication in a first frequency and to receive a signal according to a cellular communication in a second frequency at the same time. In this case, it may be required to limit the cellular communication operations in the first frequency at a time point of receiving a signal according to the sidelink operations in the second frequency.
As described above, a resource in which cellular operations are being restricted in order to allow the sidelink operations to be performed may be referred to as a sidelink gap. The sidelink gap may be requested to the serving cell by the user equipment (UE). However, it will be inefficient to unconditionally request a sidelink gap without knowing whether or not the serving cell has the capability of setting up such sidelink gap.
When the UE transmits a sidelink gap request to a serving cell, it is required to determine (or define) which types of information are to be added in order to increase efficiency.
Furthermore, in case the sidelink gap is needed in a frequency other than the current serving cell, the serving cell may not know which sidelink gap is being required by the other frequency. At this point, a problem lies in the method used for allowing the serving cell to set up the sidelink gap for the other frequency to the user equipment (UE).